We will investigate the reasons for the nonuniform behavior in smooth muscle preparations of the different actin isomers to assess whether these isomers are being use differentially to carry out specific actin-related functions. This work will make use of differential extraction and reversible crosslinking reagents. We will attempt to purify the different actin isomers in an active form and study their differential interaction with known actin binding proteins such as myosin, tropomyosin, and actinin. As a second line of investigation we will examine the acetylation and histidine methylation of actin using an in vitro protein synthesizing system and purified actin mRNA isolated from Dictyostelium discoideum. In particular, we will seek to determine if there is a requisite order for the introduction of these modifications, and we will attempt to evaluate the role of N-acetylation in actin function.